Surface studies using Monte Carlo simulations

Tan and co-workers have studied the stabilty of the c(4x4) and c(2x2) phases using Monte-Carlo simulations with Lennard-Jones potentials confirming that a de-alloying transition occurs between 0.375 and 0.50 ML [117]. Within the surface alloy model the outermost mixed layer was found to be strongly buckled with Pb atoms outermost by about 0.8 A compared with the LEED value of 0.66 A. A modulation of the top layer Cu chains was also detected in agreement with experiment. The distance between neighbouring Pb atoms was found to be bi-modal with values of 3.08 and 3.22 A compared to the experimental value of 3.4 0.15 A by LEED [113] and 3.3 0.15 A by STM [115]. 

The enantioselectivities of reactions on chiral surfaces are of interest from a practical standpoint and are the result of enantiospecific differences in reaction energetics and reaction barriers. Another manifestation of the enantiospecific interaction between a chiral adsorbate and a chiral surface is adsorbate orientation. Enantiospecific orientations of chiral adsorbates on naturally chiral metal surfaces have been predicted by molecular simulation studies. The first studies using Monte Carlo methods to study chiral cycloalkanes adsorbed on chiral surfaces pre-... 

Lin et al. used Monte Carlo simulations to study the air interface of a solvent-swollen polymer film, and found that the solvent modifies surface tensions. Lin et al. found that the solvent-swollen polymer (polymer-liquid) coexists with a solvent vapor and a solvent-rich liquid. This solvent-rich liquid, present at the air-solvent vapor interface, moderates the interaction with the air-solvent vapor. 

Ab initio molecular orbital calculations are being used to study the reactions of anionic nucleophiles with carbonyl compounds in the gas phase. A rich variety of energy surfaces is found as shown here for reactions of hydroxide ion with methyl formate and formaldehyde, chloride ion with formyl and acetyl chloride, and fluoride ion with formyl fluoride. Extension of these investigations to determine the influence of solvation on the energy profiles is also underway the statistical mechanics approach is outlined and illustrated by results from Monte Carlo simulations for the addition of hydroxide ion to formaldehyde in water. 

Computational efforts using DPT calculations as well as kinetic modeling of reactivities based on Monte Carlo simulations or mean field mefh-ods have been employed to study elementary processes on Pt surfaces. 2 228 Unraveling systematic trends in structure versus reactivity relations remains a formidable challenge due to fhe complex nafure of sfrucfural effects in electrocatalysis. 

Mitchell et al. (390) using nuclear reaction analysis (NRA), found 6 = 0.25 for the saturation adsorption of C2H4 on Pt(lll) at 100 K (also see 391). This result has been confirmed by a combined study done with NRA and XPES (392) and by STM (393-395). Furthermore, the value of 8 = 0.25 for C2H4 saturation coverage at low temperature is in agreement with a Monte Carlo simulation of QH4 adsorption on Pt(lll) by Windham et al. (396), who showed that an ensemble of four Pt surface atoms is required to absorb one C2H4 molecule. 

Recently, the kinetics of faceting was studied using a Monte Carlo simulation (109). Evaporation-condensation and surface diffusion were considered for the simple cubic crystal with nearest- and next-nearest-neighbor interactions. It was... 

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